Visualize some edges of a mesh with Blender (or MeshLab)
Blender doesn't render mesh edges, it only renders faces. While you can display the mesh edges in the 3dview and see them when using an opengl render, they will be one colour for the object, normally black or orange when selected while grouped objects will be green when selected.

There are some ways to get around this, one is to use a wireframe modifier that turns the edges into a tube like mesh structure.

You can then apply the modifier and select parts of the mesh and assign different materials as explained before.



To get both outline and faces you simply need to duplicate the object and turn the duplicate into the wireframe tubing.

I don't know if the ply importer will maintain any edge colour information, but you may be able to adjust it to automate the process if you need to work with a complex mesh.